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arXiv 2006.02073cond-mat.str-el
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Kagome反铁磁体Cd-Kapellasite中自旋和声子的热霍尔效应

Thermal Hall Effects of Spins and Phonons in Kagome Antiferromagnet Cd-Kapellasite

Masatoshi Akazawa, Masaaki Shimozawa, Shunichiro Kittaka, Toshiro Sakakibara, Ryutaro Okuma, Zenji Hiroi, Hyun-Yong Lee, Naoki Kawashima, Jung Hoon Han, Minoru Yamashita

摘要:

研究了可果美反铁磁体Cd-kapellasite(Cd-K)的热输运性质。我们发现场对纵向热导率的抑制作用在低于~25 K时出现,表明自旋对纵向热导率的贡献很大.我们还发现,在所有的Cd-K样品的自旋液相中的清晰的热霍尔信号。霍尔热导率k_xy的大小与样品的散射时间有很大的关系。另一方面,所有Cd-K样品的k_xy的温度依赖性是相似的,k_xy在几乎与声子热导率k_xy^ph的峰值相同的温度处显示出一个峰值,该峰值由k_xx在15 T处估计。这些结果表明在15 T下存在一个占主导地位的声子热霍尔k_xy^ph。除了k_xy^ph外,我们还发现k_xy在低场下的场依赖性在低温下是非线性的,伴随着k_xx的场抑制的出现,表明在低场下存在自旋热霍尔k_xy^sp。值得注意的是,通过对其他kagome反铁磁体的kxy ^sp数据的kxx依赖性的组合,我们发现,kxy ^sp在低kxx区保持恒定,而在高kxx区kxy ^sp开始随着kxx的增加而增加。kxy ^sp与k_xx的关系表明在可果美反铁磁体中自旋热霍尔效应中存在着本征和非本征机制。此外,在低场下,k_xy^ph和k_xy^sp都消失在反铁磁有序相中,表明声子本身并不表现出热霍尔效应.在~7 T以上的强场作用下,k_xy^ph随场致k_xx和比热的增加而增加,表明声子与场致自旋激发的耦合是k_xy^ph的来源。

英文摘要:

We have investigated the thermal-transport properties of the kagome antiferromagnet Cd-kapellasite (Cd-K). We find that a field suppression effect on the longitudinal thermal conductivity k_xx sets in below ~25 K, suggesting a large spin contribution k_xx^sp in k_xx. We also find clear thermal Hall signals in the spin liquid phase in all Cd-K samples. The magnitude of the thermal Hall conductivity k_xy shows a significant dependence on the sample's scattering time. On the other hand, the temperature dependence of k_xy is similar in all Cd-K samples; k_xy shows a peak at almost the same temperature of the peak of the phonon thermal conductivity k_xy^ph which is estimated by k_xx at 15 T. These results indicate the presence of a dominant phonon thermal Hall k_xy^ph at 15 T. In addition to k_xy^ph, we find that the field dependence of k_xy at low fields turns out to be non-linear at low temperatures, concomitantly with the appearance of the field suppression of k_xx, indicating the presence of a spin thermal Hall k_xy^sp at low fields. Remarkably, by assembling the k_xx dependene of k_xy^sp data of other kagome antiferromagnets, we find that, whereas k_xy^sp stays a constant in the low-k_xx region, k_xy^sp starts to increase as k_xx does in the high-k_xx region. This k_xx dependence of k_xy^sp indicates the presence of both intrinsic and extrinsic mechanisms in the spin thermal Hall effect in kagome antiferromagnets. Furthermore, both k_xy^ph and k_xy^sp disappear in the antiferromagnetic ordered phase at low fields, showing that phonons alone do not exhibit the thermal Hall effect. A high field above ~7 T induces k_xy^ph, concomitantly with a field-induced increase of k_xx and the specific heat, suggesting a coupling of the phonons to the field-induced spin excitations as the origin of k_xy^ph.

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